This phenomenon can also be observed in internal combustion engines such as in spark-ignition engines. For some time, it has been attempted to utilize the ion flow for various engine control and diagnostic functions such as for knock detection, misfire detection, phase detection, estimation of combustion pressure or the position of the pressure maximum, determination of the mixture composition and for detection of the lean running limit.
The spark plug is usually used as a measuring probe. After applying a voltage across the center electrode and ground, the ion flow can be measured after the decay of the ignition spark.
With respect to the above, the following problems occur: a current offset occurs because of the shunt resistances outside and within the spark plug (for example, contamination of the spark plug insulator). This current offset interferes with an exact detection of the ion flow generated by the combustion and this offset is to be eliminated.
No ion flow measurement is possible during the burning duration of the ignition spark. A masking can lead to signal jumps in the ion flow measurement signal which, for example, leads to erroneous detections in a subsequent knock detection. The ignition process should be masked without disturbing the measurement signal.
Methods and components realized in analog technology, such as short-term integrators, or methods and components realized in digital technology are applied to evaluate the ion flow. It is conventional to switch the measurement signals of several cylinders sequentially to these resources in order to save cost (multiplexing). The multiplexing has to be executed without crosstalk between the cylinder channels. Furthermore, it is to be prevented that the now shorter signal segments, which are specific to a cylinder, lead to a reduction in quality when making the offset correction. The improvement of the reliability and the robustness of engine control functions and diagnostic functions is achieved by utilizing these signals with improved signal to noise ratio for the feature formation.